1. Field of the Invention
This invention relates to dental and medical compositions. In particular, this invention relates to dental/medical compositions comprising degradable copolymers which are suitable for use as root canal sealants, root canal filling materials, dental restorative materials, implant materials, bone cements and pulp capping materials.
2. Description of the Related Art
Endodontic therapy for a diseased or otherwise compromised tooth generally involves the dental practitioner accessing the root canal, debriding and disinfecting the root canal to clean and remove all of the soft tissue (the pulp) therein, and then enlarging the canal to remove irregularities or rough surfaces within the canal. A pre-formed “cone” or “point” is then inserted into the canal, and the cone is laterally or vertically condensed into the canal so that the point of the cone terminates at the apex of the canal. A commonly used cone material is gutta percha, which is a thermoplastic rubber. Because of the many irregularities which remain in the surface and shape of the canal even after treatment, it is difficult to achieve a satisfactory seal between the apex of the root canal and the cone without use of a root canal filler or sealant. Numerous sealants have been described, for example swellable hydrophilic acrylates and methacrylates such as 2-hydroxyethyl methacrylate (HEMA), as disclosed in U.S. Pat. No. 3,925,895 to Kliment et al. The monomers are mixed with polymerization initiator immediately prior to use and delivered to the root where polymerization occurs in situ. U.S. Pat. No. 4,986,754 discloses an injectable endodontic filling material comprising a mixture of balata or gutta percha with a liquid plasticizer. U.S. Pat. No. 4,449,938 discloses use of a two-component, room temperature setting organopolysiloxane compositions used for dental impression materials.
Despite these advances, the most commonly used root canal sealants remain compositions comprising a mixture of zinc oxide with eugenol (ZOE), and mixtures comprising calcium hydroxide. ZOE in particular is irritating to some patients, and has low adhesion to the walls of the root canal. Root canal sealants should be non-toxic, non-irritating, radiopaque, and have no or minimal shrinkage. They should also set within a reasonable period of time. They must be biologically compatible with tooth structure, and are preferably inert to moisture and to the pH conditions found in the mouth. Ideal preparations have low viscosity to facilitate insertion into the root canal, and even more preferably, are thixotropic. In the case of overflow of root canal sealant from the apex into the surrounding tissue or structure during a filling process, the overflowed excess should be desirably absorbed by the surrounding body tissue and cause tissue growth and recovery.
In contrast to endodontic procedures, in certain other dental procedures the pulp of the tooth is left intact. Where the pulp is exposed, a “pulp capping” compound is required which will preserve the vitality of the pulp. Pulp capping compounds must also be non-toxic, and cannot result in any irritation to the pulp. Ideal pulp capping compounds also allow for regrowth of the surrounding tissue and dentine. Calcium hydroxide-based pulp capping compounds are therefore common, as described in U.S. Pat. No. 3,047,400, and in U.S. Pat. No. 4,240,832, which discloses use of condensates of alkyl salicylates with aldehydes reacted with calcium hydroxide or calcium oxide. Despite these advances in the art, there remains a need for pulp capping materials which are biocompatible, non-toxic, and which have advantageous handling properties.
Bioactive glass compositions have been proven effective in activating tissue and bone regrowth. Commercially available materials marketed under BioGlass®, PeroGlas™ and NovaBone™ trademarks available from USBiomaterials Corporation, are supplied in the form of particulates. Although these products have been shown to activate growth of tissue, the applications for the products are limited due to the nature of the particulates. The particulates can only be used for certain applications, such as filling-type applications where no near-term stress or pressure is present. U.S. Pat. No. 6,051,247 to Hench et al. is directed to moldable bioactive compositions comprising a bioactive material in combination with a polysaccharide. The compositions are moldable, but do not cure to hardened form. Accordingly, the compositions are not useful as solid-forming materials that provide strength to the area of application. There remains a need to provide bioactive materials for dental and medical applications in compositions that can provide strength and integrity to the area of application.